Reduction of parameter requirements.

* All the objects `Img<T>` used as parameters have been replaced by `RandomAccessibleInterval<T>` or `IterableInterval<T>` objects.
* A parameter `ImgFactory<T>` has been added when the creation of an `Img<T>` as an output was necessary.
* The class `Histogram<T>` from package `net.imglib2.algorithm.stats` has been copied (class HistogramZ) and the constructor parameter `Img<T> `has been change into `IterableInterval<T>`.